Tracheostomy tubes are well known. They are used to provide direct access to a patient's trachea for either forced respiration or to provide an air passage for the patient.
A type of tracheostomy tube has an outer or exterior cannula into which an inner or interior cannula is inserted. By incorporating both an outer and an inner cannula, such tracheostomy tube enables only the removal of the inner cannula for cleaning without having to remove the outer cannula tube from the patient, thereby minimizing the discomfort to the patient and the need to remove the outer cannula once it is installed in the patient's trachea.
Given that the inner cannula has to be removed from the outer cannula for purposes such as for example cleaning, or for that matter different inner cannulas be used for the patient during different times of the day, the mating of the inner cannula to the outer cannula has to be done securely and, at the same time, the inner cannula has to be readily removable from the outer cannula.
One of the prior art tracheostomy tubes that has both an inner and outer cannula is the D.I.C..TM. tracheostomy tube sold by the assignee of the instant invention. There, at least one circumferential extension is provided at the proximal end of the inner cannula so that when the inner cannula is pushed into the outer cannula, this circumferential extension comes to rest in a corresponding circumferential groove integrated to the hub of the outer cannula. It is in essence a kind of push and snap fit. However, an inadvertent movement on the part of the patient, or anyone else, could possibly cause the inner cannula to be pulled from the outer cannula.
Another tracheostomy tube secures the inner cannula to the outer cannula by providing a "twist-on lock" whereby, after the inner cannula is inserted into the outer cannula, a rotational movement of the hub of the inner cannula is effected relative to the hub of the outer cannula to secure the inner cannula to the outer cannula by means of the interaction between two bumps at the hub of the inner cannula with two internal grooves at the hub of the outer cannula. The problem with this tracheostomy tube is that since both the inner and outer cannulas are molded components, sometimes such components are not molded to exactly the correct specification. Thus, when the inner cannula, for example, is molded too thin, it can readily come loose from the outer cannula as for example when the patient coughs. On the other hand, if the inner cannula is molded too thick, the interaction between the bumps at the hub of the inner cannula and the internal grooves at the hub of the outer cannula may become somewhat tight so that when the medical personnel tries to mate the inner cannula to the outer cannula, her efforts to twist and lock the outer cannula into place with the inner cannula may cause undue discomfort to the patient.
A tracheostomy tube that provides for a secured engagement between its inner and outer cannulas, irrespective of the imperfection that may be due to the molding manufacturing process, is therefore needed. Moreover, the insertion of such tracheostomy tube to a patient should not cause a disproportionate amount of discomfort to the patient because the inner and outer cannulas may not have been produced exactly to specification.